1. Field of the Invention
The present invention relates to a suck back valve for sucking a predetermined amount of fluid flowing through a fluid passage in accordance with a displacement action of a diaphragm so that any liquid drip may be avoided, for example, at a supply port for the fluid.
2. Description of the Related Art
The suckback valve has been hitherto used, for example, in the production steps for semiconductor wafers or the like. The suck back valve has a function to avoid so-called liquid drip in which a trace amount of coating liquid drips from the supply port toward the semiconductor wafer when the supply of the coating liquid is stopped for the semiconductor wafer.
A suck back valve concerning the conventional technique is shown in FIG. 7 (see, for example, Japanese Utility Model Publication No. 8-10399).
The suck back valve 1 comprises a main valve body 5 formed with a fluid passage 4 for making communication between a fluid inlet port 2 and a fluid outlet port 3, and a bonnet 6 joined to an upper portion of the main valve body 5. A diaphragm 7, which is composed of a thick-walled section and a thin-walled section, is provided at a central portion of the fluid passage 4. The bonnet 6 is formed with a pressure fluid supply port 8 connected to an unillustrated pressure fluid supply source, for supplying compressed air for operating the diaphragm in accordance with the switching action of a selector valve (not shown).
A piston 9 is fitted to the diaphragm 7. A v-packing 10, which slides on the inner wall surface of the main valve body 5 and which functions as a seal, is installed to the piston 9. A spring 11 for always pressing the piston 9 upwardly is provided in the main valve body 5.
A screw member 12 is provided at an upper portion of the bonnet 6, for making abutment against the piston 9 in accordance with the action of increasing or decreasing the screwing amount to adjust the displacement amount of the piston 9 so that the flow rate of the coating liquid sucked by the diaphragm 7 is adjusted.
A coating liquid supply source 13 for storing the coating liquid is connected to the fluid outlet port 2 via a tube passage 14 such as a tube. An ON/OFF valve 15, which is constructed separately from the suck back valve 1, is connected between the coating liquid supply source 13 and the fluid inlet port 2. The ON/OFF valve 15 functions to make changeover between the supply state and the supply stop state of the coating liquid with respect to the suck back valve 1 in accordance with its energizing/deenergizing action thereof.
The operation of the suck back valve 1 will be schematically described. In an ordinary state, the coating liquid is supplied from the fluid inlet port 2 to the fluid outlet port 3. In this state, the piston 9 and the diaphragm 7 are displaced downwardly in an integrated manner in accordance with the action of the compressed air supplied from the pressure fluid supply port 8. The diaphragm 7, which is coupled to the piston 9, protrudes into the fluid passage 4 as shown by two-dot chain lines in FIG. 7.
When the flow of the coating liquid in the fluid passage 4 is stopped in accordance with the switching action of the ON/OFF valve 15, the supply of the compressed air from the pressure fluid supply port 8 is stopped. Accordingly, the piston 9 and the diaphragm 7 are lifted upwardly in an integrated manner in accordance with the action of the resilient force of the spring 11. A predetermined amount of the coating liquid, which remains in the fluid passage 4, is sucked in accordance with the action of negative pressure effected by the diaphragm 7. Thus, any liquid drip is avoided at an unillustrated supply port.
In this case, the suction amount of the coating liquid corresponds to the displacement amount of the piston 9. The displacement amount of the piston 9 is adjusted by the screw member 12.
The suck back valve 1 concerning the conventional technique described above includes a fluid pressure control unit 17 which is connected to the pressure fluid supply port 8 via a tube member 16 such as a tube in order to highly accurately control the flow rate of the compressed air supplied to the pressure fluid supply port 8.
However, in the case of the suck back valve 1 concerning the conventional technique described above, the suction amount of the coating liquid is adjusted manually by a skilled operator by increasing or decreasing the screwing amount of the screw member 12. For this reason, an inconvenience arises in that the suction amount of the coating liquid cannot be controlled highly accurately. In this case, the screwing amount of the screw member 2, which has been once set, has to be manually adjusted by the operator at each time corresponding to the supply amount of the coating liquid. Such an operation is complicated as well.
When the suck back valve 1 concerning the conventional technique is used, it is necessary to perform the piping connection operation between the suck back valve 1 and the fluid pressure control unit 17 and between the suck back valve 1 and the ON/OFF valve 15. Such an operation is complicated, and it is necessary to prepare an exclusive space for additionally providing the fluid pressure control unit 17 and the ON/OFF valve 15 other than the suck back valve 1. Therefore, an inconvenience arises in that the installation space is increased.
Another inconvenience arises as follows. That is, the flow passage resistance is increased due to the piping connected between the suck back valve 1 and the fluid pressure control unit 17. For this reason, the response accuracy of the diaphragm is deteriorated.
Still another inconvenience arises as follows. That is, an unillustrated driving unit is separately required to make changeover between the ON state and the OFF state of the ON/OFF valve 15. The piping connection operation is complicated between the ON/OFF valve 15 and the driving unit, and the cost becomes expensive.